Another possible target for a moonlit night? Abell 21 or SH2-274 is another planetary nebula in Gemini, in the throws of dispersion. It lies about 1500 LY from earth and is about 4 LY across. My astrobin friend
@Wouter Cazaux produced a very nice
image of this recently, showing much more structure in his longer integration and darker sky. With windier conditions last night, I decided to switch to f3.3, which is easier on the guiding, and even then only achieved an RMS ~1.5"/px, again with fairly unsteady air.
There is perhaps a hint of the OIII overlaying the Hydrogen strands, but the more dispersed top half of the nebula is lost in these short exposures and integration. I pushed up the gain to 400, which is probably optimal for this camera, but left exposures at 120s to try and suppress the background gradients from bright moon. The image is cropped on the right to remove the worst of these gradients/amp glow. I went for a less saturated colour palette.
A combination of RGB with longer subs in NB would probably be the ideal, to show off the delicate layering in medusa's hair, but this will have to wait for dark skies, and Gemini is starting to sink fast as we approach summer. Hopefully there will be some good skies under our waning moon.
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